Field displacement circulator



States Unite The invention described herein may be manufactured and usedby or for the Government of the United States of America forgovernmental purposes without the payment of any royalties thereon ortherefor.

This invention relates to electromagnetic transmission systems known ascirculators and more particularly to circulators using only rectangularwaveguides.

In many situations involving the use and distribution of radio frequencyenergy, particularly the transmission or distribution of such energy byhollow circular or rectangular piping classified as waveguide, thereexists the need for such an elementary appearing device as a switch, bymeans of which energy may be sent through selected pipes out of a group.In radar devices, the familiar T-R box is an example of such a switchwhere a single antenna is connected alternately to a transmitter and 'areceiver as indicated in FIG. 1.

Such switching of radio frequency energy is not a simple matter becausethe rapidity with which such switching occurs normally rules out anyapparatus which involves mechanical motion. In addition, efficient powertransfer and avoidance of spurious signals requires careful attention toimpedance matching even during the instant switching action occurs.

A further application of waveguide switches to radio systems such asradar is the elimination of adverse effects of return energy on thetrnasmitter. It is well known that radar energy reflected by nearbyobjects or by a mismatched antenna can return to the radar transmitterwhile it is operating, causing undesirable variable loading thereof.Thus it would be advantageous to use an additional waveguide switchbetween the transmitter and the antenna which will deliver transmitterenergy to the antenna and at the same time deliver energy returned bythe antenna to a load device where it can be absorbed harmlessly toprevent its undesirable effect upon the transmitter.

Thus two typical applications of waveguide switches have been set forth,the first being simpler in principle than the latter because the latteris required to be operative to channel energy simultaneously throughseveral paths.

A class of devices capable of fulfilling the more difficult latterrequirements has been labeled circulator, which in the past hasconsisted of one or more sections of waveguide containing gyromagneticmaterial in combination with several mode transducers. Such circulatorshave been of a first type which relies for its operation upon therotation of the plane of polarization of the propagated energy, or of asecond type, the differential phase shift type, which depends upon thenonreciprocal phase shift of a slab of ferrite in a rectangularwaveguide. For the first type, to secure rotation of the plane ofpolarization, it has been customary to use circular waveguide whereas inmost microwave transmission systems rectangular waveguide is primarilyused. Thus initially in use of this type of polarization circulator, animpedance matching problem is encountered due to the difference inimpedance of circular and rectangular waveguide. In the differentialphase shift type of circulator two hybrid junctions are required inaddition to the ferrite loaded waveguide thereby increasing the size,weight and cost of the overall circulator.

It is therefore a first object of this invention to provide a circulatorusing only rectangular waveguide.

I atet A further object is to provide a passive duplexer.

A further object of this invention is to provide a circulator whereinthe phase of the transmitted electromagnetic energy is shifted with nochange in its plane of polarization.

A further object of this invention is to provide a microwave circulatorusing only rectangular waveguide sections and a transverse magneticfield.

A further object of the present invention is to provide a circulatorrequiring no transitional devices.

It is a further object of the present invention to provide a microwavecirculator which does not require any magic Ts or hybrid junctions.

It is a further object of the present invention to provide a microwavecirculator of reduced size, weight and cost.

Other and further objects and features of the present invention will bereadily appreciated as the same becomes better understood by referenceto the following detailed description when considered in connection withthe accompanying drawings wherein:

FIG. 1 shows a typical arrangement of apparatus embodying the featuresof the present invention.

FIGS. 2-6 show various embodiments of the circulator constructed inaccordance with the teachings of the present invention.

In accordance with the basic features of the present invention,utilization is made of the principle that the field distribution in arectangular waveguide containing a ferrite subjected to a magnetic fieldcan be assymetrical even though the physical configuration issymmetrical. By properly selecting the ferrite and its proportions it ispossible to concentrate the energy on one side of the waveguide.Reversing the field or changing the direction of propagation will causethe energy to concentrate on the other side of the wave guide. Using theprinciples of the present invention this phenomenon has been utilized toconstruct a new type of circulator. Typically ferrite material is placedat the region of the junction of n rectangular waveguides whichintersect at 360/11 degrees.

The placement of the ferrite can be either in the immediate region ofthe junction which is common to all the waveguide, or it can be disposedin the waveguide in sulficient proximity to the junction or commonregion so as to affect the distribution of energy in the junction. Themagnetic field is applied normal to the broad dimension of thewaveguide. The basic apparatus of the present invention can also beemployed as a waveguide switch by using a reversible magnetic fieldinstead of a static magnetic field.

As used in connection with the present invention the term circulator isapplied to a passive device of 11 ports that may be used interchangeablyfor input or output of electromagnetic energy, the device having thepeculiar property that energy going into a first port will come out froman adjacent (second) port while energy entering the second port will notcome out at the first port but instead will come out at a subsequentadjacent (third) port, etc., with energy from the nth port finallyreturning to the adjacent (first) port.

With reference now to FIG. 2 of the drawing the typical apparatusindicated therein embodies the features of the present invention asapplied to a three port circulator with one broad wall thereof beingremoved to show inside arrangements. It is to be understood of coursethat the principles of the invention are also applicable to circulatorshaving a different number of ports. Apparatus of FIG. 2 makes use ofpropagational characteristics of a rectangular waveguide loaded byferrite wherein an asymmetrical radio frequency field distribution isobtained even though the distribution of the ferrite material itself issymmetrical. This asymmetrical field distribution is a consequence ofthe radio frequency magnetic field being elliptically polarized inplanes parallel to the broad Walls of the guide and is of opposite senseon either side of the guide. Since the effective permeability of themagnetized ferrite depends on the sense of polarization it is seen thatthe sides of the ferrite loaded guide are electrically dissimilar. Thusthe apparatus effectively displaces the field of the energy beingtransmitted through a waveguide to one side of the guide or the other insuch a way that substantially all the power being transmitted throughthe guide can be diverted into one adjacent waveguide in the junctionregion and prevented from entering other waveguides. As shown in FIG. 2,three rectangular waveguides 10, 11 and 12 intersect at angles of 120degrees in the plane of the broad dimension. In the region ofintersection which is common to all the waveguides, is disposed aferrite member 13 having three-fold symmetry. A permanent magnet fieldproducing device of suitable structure indicated by numeral 14 isprovided to apply a'magnetic field to the ferrite material 13perpendicular to the plane of FIG. 2. It is to be understood of coursethat in applications wherein a static field is suitable, the ferritematerial 13 could be permanently magnetized or a permanent magnet couldbe contained within the ferrite material itself thereby eliminating therequirement for an external magnet 14. Additionally the magnet 14 couldbe an electromagnet rather than a permanent magnet to provide somewhatmore flexible control of the operation of the device. Also the genericterm ferrite is used to define materials having gyromagnetic properties,which may be typically ferrites having spinel structure and garnetstructure.

In typical S band equipment operating at approximately 3,000 megacycles,a magnetization field intensity of 38 oersteds is sufiicient which mayeasily be provided by a small permanent magnet located either externalor internal relative to the waveguide. As further detail of a specificstructure employed, the ferrite material as shown in "FIG. 2 in the formof an equilateral triangle assembly has a dimension on the side of 1.2inches and extends between the broad walls.

With reference now to FIG. 3 of the drawing, the apparatus indicatedtherein is similar to that of FIG. 2 differing in the specificconfiguration of the ferrite member. In this particular illustration theferrite member is a cylinder 20 placed at the 120 junction of the threerectangular waveguides. Typical cylinder diameters for x-band range from.125 inch to .500 inch. The best results appeared to be obtained with adiameter of .350 inch filling the .400 inch thick guide in height. Withsuch a ferrite configuration the insertion loss of the apparatus wasless than /2 db and the isolation and reflection greater than 30 db overa frequency band of about 50 megacycles.

FIG. 4 shows a third form of ferrite loading which also has .the desiredthree-fold symmetry. In this apparatus as intended for use at thetypical X band, six slabs 21, 22, 23, 24, 25, and 26 were disposed alongthe narrow walls of the waveguides in the region of the intersection,the slabs being of .500 inch in length, .125 inch in thickness, andextending from wall to wall (broad wall).

FIG. shows a four port circulator constructed by placing two three portcirculators 30 and 31 of FIG. 2 together with an interconnection bymeans of a common waveguide from each circulator. Such a circulator maytypically have a junction separation 31 as small as /2 guide wavelength.Losses of the order of db with reflection and isolation greater than 18db from 9200 to 9400 megacycles are readily obtainable.

FIG. 6 shows an additional circulator configuration where the principlesof the present invention are applied to a four port circulator, thevarious arms of the ports being separated by 360/4 or 90 degrees.Waveguide dimensions are substantially the same as those conventionallyemployed for frequencies typically as outlined for X band in thepreceding illustrations, thus the apparatus ofFIG. 6 employs fourwaveguides 35, 36, 37 and 38 intersecting at 90 degrees, FIG. 6 showinga view taken in the broad dimension of the waveguides. Four cylindricalsections of ferrite are employed. For X-band with a waveguide innerwidth of 0.9 inch, the cylinders are centrally disposed relative to thelongitudinal axes of the Waveguide, are 0.3 inch in diameter and arespaced 0.876 inch as measured along the longitudinal axis extendingthrough opposite waveguides. The result is an arrangement wherein theferrite material is partly within the region common to all fourwaveguides and partly in the waveguides in the region near such commonregion. Such a device as FIG. 6 provides low losses with isolation andreflection of the same order as that typified in connection with thepreviously described figures.

Although the apparatus of the present invention is more likely to beused with a relatively small number of ports, typically the three orfour shown in the various figures thus far described, it is to beunderstood that the basic principles of the invention may be applied todevices employing a greater number of ports for which appropriateintersection angles and configurations of the ferrite post would beemployed. For example, it would be a logical extension of the principlesof the invention to provide for five port intersection or greaternumbers should the need arise. In any event, each waveguide leading toor from the junction is counted so that the arrangement of FIG. 6 isconsidered a four port circulator even if it is constructed from twocrossing Waveguides which are cut and then attached together in thecommon region.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. A circulator comprising, three waveguides having their longitudinalaxes in the same plane intersecting at equal angles enclosing a commonregion shared by the waveguides, ferrite material disposed in thecirculator in at least a part of a region consisting of the commonregion and portions of the waveguides contiguous, thereto, and means formagnetizing the ferrite material to such degree that energy incident ata first waveguide leaves at a second waveguide, energy incident at thesecond Waveguide leaves at the third waveguide, energy incident at thethird waveguide leaves at the first waveguide.

2. A circulator comprising, three waveguides having their longitudinalaxes in the same plane intersecting at equal angles enclosing a commonregion shared by the waveguides, ferrite material disposed in thecirculator in at least a part of a region consisting of the commonregion and portions of the waveguides contiguous thereto, said ferritepossessing symmetry for all waveguides, and means for magnetizing theferrite material to such degree that energy incident at a firstwaveguide leaves at a second waveguide, energy incident at the secondwaveguide leaves at the third Waveguide, energy incident at the thirdwaveguide leaves at the first waveguide.

3. A circulator comprising, three waveguides intersecting at equalangles. in the same plane enclosing a common region shared by thewaveguides, ferrite material disposed in the circulator in the commonregion, and means for magnetizing the ferrite material to such degreethat energy incident at a first waveguide leaves at a second waveguide,energy incident at the second waveguide leaves at the third waveguide,energy incident at the third waveguide leaves at the first waveguide.

4. A circulator comprising, three rectangular waveguides intersecting atequal angles to enclose a common region shared by all waveguides, the Hplane of said waveguides and said common region being coincident,ferrite material disposed in the circulator in at least a part of aregion consisting of the common region and contiguous portions of theWaveguides, said ferrite possessing symmetry for all. waveguides, andmeans for magnetizing the ferrite material to such a degree that energyincident at a first waveguide leaves at a second waveguide, energyincident at the second waveguide leaves at the third Waveguide, energyincident at the third waveguide leaves at the first Waveguide.

5. A circulator comprising, three rectangular Waveguides intersecting atequal angles to enclose a common region shared by all waveguides, the Hplane of said Waveguides and said common region being coincident,ferrite material disposed in the circulator in the common region, saidferrite material having a circular crosssection in said H plane of thewaveguides, and means for magnetizing the ferrite material to suchdegree that energy incident at a first waveguide leaves at a secondwaveguide, energy incident at the second waveguide leaves at the thirdwaveguide, energy incident at the third waveguide leaves at the firstwaveguide.

6. A circulator comprising, three rectangular waveguides intersecting atequal angles to enclose a common region shared by all waveguides, the Hplane of said waveguides and said common region being coincident,ferrite material in slab form disposed adjacent to the Walls of saidwaveguides perpendicular to the H plane in the common region, and meansfor magnetizing the ferrite material to such degree that energy incidentat a first waveguide leaves at a second waveguide, energy incident atthe second Waveguide leaves at the third waveguide, energy incident atthe third Waveguide leaves at the first waveguide.

7. A circulator comprising, three rectangular waveguides intersecting atequal angles to enclose a common region shared by all Waveguides, the Hplane of said waveguides and said common region being coincident,ferrite material disposed in the circulator in the common region, saidferrite material possessing symmetry for all waveguides, and magneticfield producing means external to the waveguides for magnetizing theferrite material to such degree that energy incident at a firstWaveguide leaves at a second waveguide, energy incident at the sec- 0ndWaveguide leaves at the third Waveguide, energy incident at the thirdwaveguide leaves at the first waveguide.

8. A circulator comprising, three rectangular waveguides intersecting atequal angles to enclose a common region shared by all waveguides, the Hplane of said Waveguides and said common region being coincident,ferrite material disposed in the circulator in the common region, saidferrite material possessing symmetry for all waveguides and magneticfield producing means disposed Within the waveguide for magnetizing theferrite material to such degree that energy incident at a firstWaveguide leaves at a second waveguide, energy incident at the secondwaveguide leaves at the third waveguide, energy incident at the thirdWaveguide leaves at the first Waveguide.

References Cited in the file of this patent UNITED STATES PATENTS2,794,172 Kock May 28, 1957 2,848,688 Fraser Aug. 19, 1958 2,849,687Miller Aug. 26, 1958 2,867,772 Allen Ian. 6, 1959 2,870,418 Hewitt Jan.20, 1959 2,978,649 Weiss Apr. 4, 1961 3,015,787 Allin et al. Jan. 2,1962 3,018,443 Bloom et al Jan. 23, 1962 OTHER REFERENCES Chang et al.:Proceedings of the IRE, July 1958, pages 1383-1386.

Swanson et al.: 1958 IRE Wescon Convention Rec- 0rd, Part 1, pages151-156.

Weiss: Physical Review, July 1, 1957, page 317.

Electrical Manufacturing, February 1959, pages 61- 3.

Auld: IRE Transactions on Microwave Theory and Techniques, April 1959,pages 238246.

1. A CIRCULATOR COMPRISING, THREE WAVEGUIDES HAVING THEIR LONGITUDINAL AXES IN THE SAME PLANE INTERSECTING AT EQUAL ANGLES ENCLOSING A COMMON REGION SHARED BY THE WAVEGUIDES, FERRITE MATERIAL DISPOSED IN THE CIRCULATOR IN AT LEAST A PART OF A REGION CONSISTING OF THE COMMON REGION AND PORTIONS OF THE WAVEGUIDES CONTIGUOUS THERETO, AND MEANS FOR MAGNETIZING THE FERRITE MATERIAL TO SUCH DEGREE THAT ENERGY INCIDENT AT A FIRST WAVEGUIDE LEAVES AT A SECOND WAVEGUIDE, ENERGY INCIDENT AT THE SECOND WAVEGUIDE LEAVES AT THE THIRD WAVEGUIDE, ENERGY INCIDENT AT THE THIRD WAVEGUIDE LEAVES AT THE FIRST WAVEGUIDE. 